NDRLS frequently asked questions

What is a diagnostic reference level?

Diagnostic Reference Levels (DRLs) are a form of investigation level [1]. Perhaps the most succinct definition comes from the Council of the European Union, which stated that DRLs are dose levels that “are expected not to be exceeded for standard procedures when good and normal practice regarding diagnostic and technical performance is applied” [2].

Diagnostic Reference Levels are set at regional or national level, a reflection that there is a wide variation in medical practice between regions.

Importantly, a DRL is not a regulatory limit on the dose that can be administered to a patient, it is simply an indicative value. If the dose delivered by an imaging facility consistently exceeds the DRL, it is an indication that the facility should further optimise their scanning protocols.

How are DRLs calculated?

There is no universal method used to calculate DRLs. However, in radiographic imaging, the basic principle is that the DRL should be a reflection of common practice within a given geographical region. In Australia, ARPANSA has helped develop (or is in the process of aiding the development of) DRLs at a national level (NDRLs).

ARPANSA has adopted the approach of calculating DRLs based on the results of wide-scale surveys of Australian imaging facilities. In the case of Multi-Detector CT (MDCT) studies on adult patients, the present DRLs were calculated using surveys submitted to the National DRL Service during 2011.

Each survey submitted was used to calculate the participants Facility Reference Level for a given protocol. The DRL was then based on the 75th percentile (third quartile) of the resulting FRL distribution.

What is a facility reference level?

A facility reference level (FRL) is the median dose delivered to a standard patient undergoing a specific routine diagnostic exposure at a given facility. FRLs can be used to:

  • define local facility doses for common procedures

  • compare doses between similar protocols

  • assess the dose impact of the introduction of new protocols

  • compare doses between facilities

  • compare with regional or national DRLs

  • provide a comparative dose metric for optimisation strategies

  • indicate compliance with state and territory regulatory requirements.

The following diagram demonstrates the relationship between an FRL for a particular scan and the national DRL for that scan.

Relationship between an FRL for a particular scan and the national DRL

What is the purpose of DRLs?

The objective of a diagnostic reference level is to help avoid excessive radiation dose to the patient that does not contribute additional diagnostic information to the medical imaging task [3].

A diagnostic reference level can be used to:

  • improve local, regional, or national distributions of observed doses for a general medical imaging task, by reducing the frequency of unjustified high or low dose values
  • promote an optimum range of doses for specified medical imaging protocols
  • provide a common dose metric for the comparison of FRLs between facilities, protocols and modalities
  • indicate compliance with the relevant state and territory regulatory requirements [4].

DRLs can only be effective if appropriate local review and action is undertaken when the doses observed are consistently outside the selected diagnostic reference level.

What are the regulatory requirements?

State and territory regulatory bodies require implementation of the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) Code of Practice (RPS 14) [4] which requires the development and application of diagnostic reference levels.

The ARPANSA Code of Practice (RPS 14), Section 3.1.8 states that:

"the Responsible Person must establish a program to ensure that radiation doses administered to a patient for diagnostic purposes are:

a. Periodically compared with diagnostic reference levels (DRLs) for diagnostic procedures for which DRLs have been established in Australia; and

b. If DRLs are consistently exceeded, reviewed to determine whether radiation has been optimised."

In addition, the ARPANSA Safety Guide [5], Section 7.8, suggests that:

"as part of the QA program, patient dose surveys are undertaken periodically to establish that the doses are acceptable when compared with published DRLs."

The Department of Health (DoH) Diagnostic Imaging Accreditation Scheme (DIAS), the Royal Australian & New Zealand College of Radiology (RANZCR) Quality and Accreditation Program and the Australian College on Healthcare Standards (ACHS) EQuIP 5 Accreditation Standards all require compliance with state and territory regulation which in turn requires compliance with the ARPANSA Code of Practice (RPS.14).

What are the Australian National MDCT diagnostic reference levels?

ARPANSA, in collaboration with other stakeholders, has developed the National DRL Service which facilities can use to compare their doses with the national DRLs and from which dose data will be used to develop and update national DRLs.

Due to its significantly higher population dose contribution, the National DRL Service was initially applied to Multi-Detector CT (MDCT) imaging. It is expected that DRLs for Nuclear Medicine, Mammography and Image Guided Interventional Procedures will be published in late 2016.

Australian National MDCT diagnostic reference levels for adult and paediatric patients are shown in Tables 1a-c.

The scan region for each protocol is shown at Modality surveys - before you enter data.

Table 1a:   Australian adult (15+ years) MDCT DRLs
Australian adult (15+ years)
MDCT diagnostic reference levels
Adult
Protocol
DLP
(mGy.cm)
CTDI vol
(mGy)
Head 1000 60
Neck 600 30
Chest 450 15
AbdoPelvis 700 15
ChestAbdoPelvis 1200 30
Lumbar Spine 900 40


For more information see Adult DRLs information.

Table 1b:   Australian child (5-14 years) MDCT DRLs
Australian child (5-14 years)
MDCT diagnostic reference levels
Child
Protocol
DLP
(mGy.cm)
CTDI vol
(mGy)
Head 600 35
Chest 110 5
AbdoPelvis 390 10


For more information see Paediatric DRLs information.

Table 1c:   Australian baby/infant (0-4 years) MDCT DRLs
Australian baby (0-4 years)
MDCT diagnostic reference levels
Baby
Protocol
DLP
(mGy.cm)
CTDI vol
(mGy)
Head 470 30
Chest 60 2
AbdoPelvis 170 7

Why is the adult CTDIvol NDRL for the ChestAbdoPelvis protocol high?

The MDCT NDRLs were calculated from data submitted to ARPANSA in 2011. During this time, it would appear that a number of facilities were incorrectly supplying the CTDIvol data. Rather than submitting the average of the CTDIvol for the two phases of the protocol, they submitted the sum. As a result, the NDRL is double what it should be. Although the NDRL will continue to be 30 mGy for Chest/Abdo/Pelvis protocols until the next formal review of the DRLs, you should use the figure of 15 mGy for the purposes of comparison.

How were the MDCT adult DRLs calculated?

Data submitted during the first year of operation of the ARPANSA DRL service (2011) were used to set the current MDCT Adult DRLs. The Facility Reference Level (see above) from each submitted survey was calculated and the 75th percentile of the distribution of FRLs for each protocol type was used as the basis of the DRL.

How were the MDCT paediatric DRLs calculated?

At the end of July 2012, ARPANSA was given access to paediatric MDCT dosimetry data collected in a survey of paediatric facilities in Australia carried out by the Royal Australian and New Zealand College of Radiologists (RANZCR). Sufficient paediatric data were submitted for ARPANSA to calculate paediatric DRLs for baby and child cohorts for Head, Chest and AbdoPelvis protocols.

Due to differences in the surveyed scan parameters it was not possible to directly import the RANZCR data into the ARPANSA database and insufficient data was generated per facility for ARPANSA to be able to generate individual Facility Reference Levels (FRL). However four fields, kVp, girth (cm), CTDIvol (mGy) and DLP (mGy.cm) were able to be used in this analysis.

How do I compare my facility’s CT doses to the NDRLs?

ARPANSA provides a free service for you to compare the doses your facility delivers to the National Diagnostic Reference Levels for common CT protocols. It was this platform that was used to set the NDRLs initially, and it will be used to update the NDRLs in the future. Using the ARPANSA service is not mandatory; if you wish to use a different service, or wish to conduct the comparison yourself, you can still fulfil the regulatory requirements.

You should compare your Facility Reference Level (FRL) - which is the median dose delivered to patients undergoing a given protocol at your facility - to the DRLs (see above). The median dose is simply the value in the middle of the distribution of delivered doses, i.e. the same number of scans will deliver a dose above the median as deliver a dose below the median.

The NDRLs were defined by calculating the 75th percentile of the FRLs submitted to ARPANSA during 2011. If your FRL is above this value, it suggests that you are delivering a higher dose than 75% of your colleagues throughout Australia. To calculate your FRL:

  • Record the CTDIvol, DLP and patient weight for a minimum of 10, but preferably 20 or more, scans performed using the same protocol on different patients. The sample should be representative of your normal patient cohort (with regards to gender, weight and age). In general, a larger number of patients will provide a better estimate of your FRL:
    • 10 patients may provide reasonable precision for head scans
    • 20 or more patients should be used for torso scans
  • Excel and other spreadsheet based applications have built in functions to determine the median, but if need be you can calculate it manually:
    • Sort the scans in terms of increasing CTDIvol.
    • If there are an odd number of patients, the median CTDIvol is the value in the middle of the list.
    • If there is an even number of patients, then the median is simply the average of the middle two values.
    • Repeat the process for DLP. Note that the median CTDIvol may not be associated with the same patient(s) as the median DLP, so the list may have to be sorted a second time to determine the median DLP.

In order to prove that you have complied with RPS 14, Section 3.1.8 a)[4] you should document your results. This documentation should include:

  • The individual patient data,
  • A brief description of the imaging parameters used (the kVp, target mAs, pitch etc.),
  • The chosen scan region, and
  • Your FRL and the corresponding NDRL.

What do I do if my facility exceeds the DRL?

Section 3.1.8 b) [4] of RPS 14 states that you should review your imaging protocols if the NDRLs are consistently exceeded. In practice, this means that if your FRL exceeds the DRL, a review is required. If the review necessitates the need for optimisation of your scans, you should perform this in collaboration with an experienced diagnostic imaging medical physicist (DIMP).

If the review necessitates the need for optimisation of your scans, you should perform this in collaboration with an experienced diagnostic imaging medical physicist (DIMP).

What CTDIvol and DLP do I use when I am using a multiple phase protocol?

  • Sum the DLP
  • Average the CTDIvol

Where’s the information on other modalities?

ARPANSA is in the process of developing DRLs for image-guided interventional procedures, mammography and nuclear medicine. When this work is ready to be published, we will update this web page with information relating to these other modalities.

Examples of UK and European DRLs

Table 2: UK & EU MDCT DRLs [6] - Comparison of Head, Chest, and Abdominal CT Dose Values with DRLs Given in European Guidelines
Examination Mean Value 3rd-Quartile Value United Kingdom Study
(3rd-Quartile Value)
European DRL
Head CT        
   CTDIw (mGy) 39 47 66 60
   DLP (mGy.cm) 544 527 787 1050
Chest CT        
   CTDIw (mGy) 9.3 9.5 17 30
   DLP (mGy.cm) 348 447 488 650
Abdominal CT        
   CTDIw (mGy) 10.4 10.9 19.0 35
   DLP (mGy.cm) 549 696 472 780

Note: Data are mean and 3rd quartile values for the examinations performed in the entire patient sample.  CTDIw – weighted CT dose index.

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Table 3:   Recommended diagnostic reference doses for general radiography for individual radiographs on adult patients [7]
Radiograph ESD per radiograph
(mGy)
DAP per radiograph
(Gy cm2)
Skull AP/PA 1.8 0.8*
Skull LAT 1.1 0.5*
Chest PA 0.15 0.1
Chest LAT 0.5 0.3*
Thoracic spine AP 3.5 1
Thoracic spine LAT 7 1.5
Lumbar spine AP 5.7 1.5
Lumbar spine LAT 10 2.5
Lumbar spine LSJ 26* 2.6*
Abdomen AP 4 2.5
Pelvis AP 4 2.2

Note: Adult is defined as a person of average size (70 to 80 kg). * = 2005 HPA Data

Table 4:   Recommended diagnostic reference doses for fluoroscopic/interventional examinations on adult patients. [7]
Examination DAP per exam
(Gy.cm2)
Fluoroscopy time per exam
(mins)
Barium (or water soluble) swallow 7.5 2.1
Barium meal 12 2.6
Barium follow through 8.4 2
Barium (or water soluble) enema 21 2.6
Small bowel enema 23 8.9
Biliary drainage/intervention 43 14
Femoral angiogram 56 5.9
Hickman line 3 1.5
Hysterosalpingogram 2 0.7
IVU 14 -
MCU 7 1.6
Nephrostogram 9 3.9
Nephrostomy 13 6.7
Retrograde pyelogram 8* 3
Sialogram 2.8 1.5
T-tube cholangiogram 5 1.8
Venogram (leg) 7* 2.2*
Coronary angiogram 31 4.3
Oesophageal dilation 13 5
Pacemaker implant 7 6

* = 2005 Data

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Table 5:   Recommended fluoroscopic/interventional diagnostic reference doses for complete examinations on paediatric patients [7]
Examination Standard age (y) DAP per exam (Gy.cm2)
MCU 0 0.1
  1 0.3
  5 0.3
  10 0.4
  15 0.9
Barium meal 0 0.1
  1 0.2
  5 0.2
  10 0.7
  15 2
Barium swallow 0 0.2
  1 0.4
  5 0.5
  10 1.8
  15 3
Table 6: Recommended diagnostic reference levels for CT examinations (CTDIvol and DLP ) [8]
vol and DLP)" width="100%">
Patient group Scan region CTDI vol (mGy)
single slice/
multi slice
DLP mGy.cm)
Single slice/
multi slice
Adults Brain
Abdomen (liver metastases)
Abdomen &pelvis (abscess)
Chest, abdomen & pelvis (lymphoma staging or follow up)
Chest (lung cancer)
Chest Hi-res
55/65
13/14
13/14
22/26

10/13
3/7
760/930
460/470
510/560
760/940

430/580
80/170

Children
0-1 yr old

5 year old

10 year  old

 


Head
Thorax
Head
Thorax
Head
Thorax
30
12
45
13
50
20
270
200
470
230
620
370

Dose values for adults relate to the 16cm diameter CT dosimetry phantom for examinations of the head and the 32cm diameter CT dosimetry phantom for examinations of the trunk.

All dose values for children relate to the 16 cm diameter CT dosimetry phantom.

Table 7: Recommended diagnostic reference level for mammography for a typical adult patient


For film screen examinations using a grid, the mean glandular dose (MGD) is 2 mGy based on the 4.2 cm acrylic American College of Radiologists phantom [9].

Additionally for Digital Mammography, the MGD shall be ≤ 1 mGy for 2.0 cm PMMA (2.3 cm 50% adipose, 50% glandular breast) and ≤ 4.5 mGy for 6.0 cm PMMA (6.5 cm 50% adipose, 50% glandular breast ) [10]

Table 8: Sample Australian nuclear medicine administered activities
Procedure name Nuclide Chemical form Route of administration Most common
activity [11] (Mode) (MBq)
Adult
reference
activity [11](MBq)
Effective
whole body
dose [12] (mSv)
Bone Scan Tc-99m MDP, HDP iv 800 900 5.1
Myocardial
perfusion
-
2 day stress/rest (stress)


Tc-99m


MIBI


iv


600


900


7.1
Myocardial
perfusion
-
2 day stress/rest (rest)


Tc-99m


MIBI


iv


600


840


7.6
Thyroid Tc-99m pertechnetate iv 200 200 2.6
Lung perfusion Tc-99m MAA iv 200 200 2.2
Renal scan Tc-99m MAG3 iv 300 350 2.5

References

  1. ICRP. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP 2007; 37:1-332
  2. European Commission. The Health Protection of Individuals Against the Dangers of Ionizing Radiation in Relation to Medical Exposure. Council Directive 97/43/Euratom,OJ L180 p22 . Luxemburg, 1997
  3. ICRP. Diagnostic reference levels in medical imaging: review and additional advice. Ann ICRP 2001; 31:33-52
  4. ARPANSA. RPS 14. Code of Practice for Radiation Protection in the Medical Applications of Ionizing Radiation. Yallambie: Australian Radiation Protection and Nuclear Safety Agency, 2008
  5. ARPANSA. RPS 14.1 Safety Guide for Radiation Protection in Diagnostic and Interventional Radiology. Yallambie: Australian Radiation Protection & Nuclear Safety Agency, 2008
  6. Tsapaki V, Aldrich JE, Sharma R, et al. Dose reduction in CT while maintaining diagnostic confidence: Diagnostic reference levels at routine head, chest, and abdominal CT-IAEA-coordinated research project. Radiology 2006; 240:828-834
  7. Hart D, Hillier MC, Shrimpton PC. Doses to patients from radiographic and fluoroscopic X-ray imaging procedures in the UK : 2010 review. Didcot: Health Protection Agency, 2012
  8. Shrimpton PC, Hillier MC, Lewis MA, Dunn M. National survey of doses from CT in the UK: 2003. Br J Radiol 2006; 79:968-980
  9. Craig A, Heggie J, McLean I, Coakley A, Nicoll J. Recommendations for a mammography quality assurance program [ACPSEM Position Paper]. Australas Phys Eng Sci Med 2001; 24:107-131
  10. BreastScreen Australia monitoring report 2006-2007 and 2007-2008. In: Cancer Series: Australian Institute of Health and Welfare, 2010
  11. Botros G, Smart RC, Towson JE. Diagnostic reference activities for nuclear medicine procedures in Australia and New Zealand derived from the 2008 survey. ANZ Nuclear Medicine 2009; 40:2-11
  12. ICRP. Radiation dose to patients from radiopharmaceuticals, Publication 80. In: Ann ICRP. Oxford, UK: ICRP, 1998

Further information on International Best Practice for Radiation Protection of Patients can be found on the International Atomic Energy Agency Radiation Protection of Patients website, which can be accessed via the following link:

IAEA Radiation Protection of Patients (RPOP):

IAEA Radiation Protection of Patients Logo